Yeah, Desann's not a full-blown Sith lord/master, he's just a Dark Jedi. I've pondered from time to time what the difference is between Dark Jedi and Sith, and I think I've come up with a fairly reasonable theory:

Sith: The Sith follow the teachings and beliefs of the Sith order to the letter. The Sith draw purely upon the dark side of the Force as is dictated by their order. Though they originally wielded purple lightsabers, all "modern" (4,000 years before Episode IV and later) Sith use red lightsabers. Moreover, "modern" Sith have adopted the title of "Darth" before their name, though that wasn't always the case (Exar Kun never had a "Darth" title during the Great Sith War). After Darth Bandon overhauled Sith customs 2,000 years ago, there have been only two Sith alive at any given time, one master and one apprentice.

Dark Jedi: The Sith are evil; Dark Jedi on the other hand are amoral. Dark Jedi are Force-sensitive individuals who do not follow the teachings of the Jedi or the Sith.

Since Dark Jedi are not bound by the same rules as the Sith, they aren't limited to using only one side of the Force. They call upon the powers of both light and dark, whatever it takes to suit their needs. This explains why some of Jerec's Dark Jedi used light side powers in Jedi Knight. Additionally, Dark Jedi don't have to worry about lightsaber colors. This explains why six of the seven Dark Jedi in JK don't have red lightsabers. Due to a lack of any structure or code, Dark Jedi tend to be weaker than their Jedi and Sith counterparts. Since there is no numerical limit to the number of Dark Jedi, their numbers can be as few as one or two to as many as thousands or even tens of thousands, as the Reborn, Shadowtroopers and Cultists in JO and JA proved.